High frequency converter arrangement



1934- w. A. HARRIS 1,970,961

HIGH FREQUENCY CONVERTER ARRANGEMENT Filed Oct. 21, 1933 INVENTOR W/ ARR/5 BY l r H I ATTORNEY 05 tion of such a Patented Aug. 21, 1934 PATENT QFFlCE HIGH FREQUENCY CONVERTER ARRANGEMENT William Arthur Harris, Belleville, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application October 21, 1933, Serial No. 694,599

6 Claims. (01. 250-) This invention relates to a high frequency changer or converter and more especially to one used as the first detector in a short wave superheterodyne receiver for modulated waves.

5 It is an object of the invention to provide such a converter in which the local oscillations are produced by the same vacuum tube which amplifies the incoming signal frequencies.

A further object is to cause the oscillator sec- 5 wave lengths such as 5 meters, where the transconductance of the oscillator section is low, by means of a triode connected in parallel with the 5 oscillator section.

A still further object of the invention is to increase the conversion conductance of a pentagrid frequency converter by means of a vacuum tube having certain of its elements connected in parallel with certain of the electrodes of the contube to operate effectively at short '0 verter.

Other objects of the invention will become apparent to those skilled in the art as the description thereof proceeds. The novel features of the invention are set forth in particularity in the appended claims, the invention itself, however,

will best be understood by reference to the following description taken in connection with the drawing in which I have indicated diagrammatically a circuit arrangement whereby my invention may be carried into effect. In the drawing,

Figure 1 is a schematic circuit arrangement embodying the invention; and,

Figure 2 is a schematic showing of the arrangement of the several electrodes of the frequency converter tube.

Referring to Fig. 1 the incoming signal currents received on antenna 20 may be transferred to the grid of the screen grid amplifier 24 by primary 21 and secondary 22 of a radio frequency transformer,

the secondary being tunable to the signal frequency by any preferred means such as the adjustable condenser 23. The output or plate circuit 25 of amplifier 24 may be connected by primary 26 and secondary 2'7 of a radio frequency transformer to the cathode C and control grid 4 of the first detector or frequency converter D which may be a multi-grid tube of the type commercially known as RCA-2A7, RCA-6A7 or RCA-1A6. The coil 27 may be tuned to the signal frequency by variable condenser 28 and a suitable grid bias on grid 4 be provided by any means such as a battery 29. The oscillator section of the converter comprising cathode C, grid 1 and oscillator element or plate 2 is effectively screened from the signal control grid 4 by means of the separate grids 3 and 5 which may be connected together within the tube envelope as shown to form a screen grid which also serves to screen the grid 4 from the plate P. Battery 38 serves to apply a high positive potential to the screen grid 3, 5 and also a positive potential to the oscillator plate 2 through the lead 37 and feedback coil 36. Coil 36 is shown inductively coupled to coil 34 which is tuned to the desired oscillator frequency by tuning condenser 35 one end of which is connected to cathode C by lead 44 and the other end to grid 1 through condenser 11 and lead 45. A grid leak resistor 10 having a value of about 50,000 ohms is shown connected between grid 1' and cathode C. A suitable value for condenser 11 is from 50 to 100 micromicrofarads. The intermediate frequency energy of the plate circuit P is shown as transferred to a pair of output terminals 43 by primary 40 and secondary coil 41 which may be tuned to the desired intermediate frequency by condensers 39 and 42 respectively. The terminals 43 are connected to the intermediate frequency amplifier of the superheterodyne by means (not shown) well known in the art, the intermediate frequency amplifier, first detector and audio frequency amplifier of the receiver may be of well known type and therefore need not be illustrated herein.

I have found that when receiving signals on wavelengths below about 30 meters, it is practically impossible to get the oscillator section of the tube with the circuit arrangement above de scribed to oscillate at a frequency high enough to provide a suitable heterodyne frequency for the incoming signals. It is believed that this is due to the low value of the transconductance of the oscillator section of the converter which in the case of the RCA 1A--6 tube I have found that it is about 400 micromhos. I have further found that by connecting a triode tube in parallel with the oscillator section of the converter, as shown, the combination will oscillate at the desired high frequency. It will be noted that no additional circuit elements are required to so connect the triode, its grid 31 being connected to lead 45 and its plate 32 to lead 33. When RCA 1A6 is used as the converter, which requires a 2.0 volt filament supply voltage, I have found that an RCA 30 tube may be satisfactorily used as the triode this tube requiring the same filament supply voltage and the same battery 46 or other voltage source may then be used to supply filament current, the filaments of the two tubes being connected in parallel.

The arrangement described has been satisfactorily used up to a frequency of 60 megacycles,

corresponding to a wavelength of about 5 meters. When receiving 12 meter Waves I may set the oscillator to oscillate at a frequency greater than the signal frequency by about 450 kilocycles, in which case the circuits including coils 40 and 41 are preferably tuned to a frequency of 450 kilocycles. As the RCA 30 tube has a transconductance of 1200 micromhos and as its transconductance is additive to that of the oscillator section of the converter, the total transconductance of the arrangement described is about 1600 micromhos.

The characteristics of the combination shown are substantially the same as those of the pentagrid converted alone, except for the higher transconductance and the higher capacities in the oscillator section. The highest frequencies at which the arrangements described may be used are approximately the same as those at which the triode will oscillate, since the additional capacitance added to the circuit by the triode will be offset by the additional transconductance obtained from the oscillator portion of the converter.

I have further found that the arrangement described gives a translation gain which is high and compares favorably with that obtainable from the converters operating alone at broadcast frequencies.

The addition of the triode to the circuit as described increases the voltage swing of the oscillator grid 1, thus causing a greater change in the plate current of the converter or causing it to provide a higher amplification of the applied voltage. Its addition also permits the converter to function at much higher frequencies than it would otherwise and thus greatly extends its range of utility.

As shown diagrammatically in Fig. 2 the oscillator anode or plate of the converter comprises two vertical rods 2 which are connected together at their base within the tube by a lead (not shown) and are located in the plane of the filament F between the oscillator grid 1 and the screen grid 3.

Having described my invention, what I claim and desire to secure by Letters Patent is:

1. In a superheterodyne receiver, the combination of a combined oscillator-detector having a cathode, an oscillator grid, an oscillator anode, a signal control grid and a plate, an output circuit connecting said plate and cathode, a circuit connecting said signal control grid and cathode, means for impressing signal currents on" said last named circuit, a tunable circuit connecting said oscillator grid and cathode, a feedback circuit coupled to said tunable circuit and connecting said oscillator anode and said cathode, and a vacuum tube having a cathode, control grid and plate, the cathode being connected to the cathode of the detector, the control grid being connected to the said oscillator grid and the plate being connected to said oscillator anode.

2. In a converter for high frequency waves, the combination of a detector having a cathode, an oscillator grid, an oscillator anode, a signal control grid and a plate, a shielding grid located between said oscillator anode and said signal control grid, an output circuit connecting said plate and cathode, means for impressing signal currents on said signal control grid, a grid circuit connecting said oscillator grid and cathode, a circuit connecting said oscillator anode and cathode and including a feedback connection to said last named grid circuit, and means for assisting in the production of local oscillations comprising a vacuum tube having its cathode connected to the cathode of said detector, its grid connected to the said oscillator grid and its anode connected to said oscillator anode.

3. In a device of the class described, the combination of a vacuum tube having a cathode, a signal control grid and a plate, an output circuit connecting said cathode and plate, means for impressing signal currents of high radio frequency between said signal control grid and. cathode, an oscillator anode and an oscillator grid located between said signal control grid and said cathode, and means for increasing the transconductance between said oscillator grid and anode comprising a vacuum tube having a cathode, a grid and a plate, a conductive connection between the cathodes of said tubes, a conductive connection between the plate of said last named tube and said oscillator anode and a conductive connection between the grid of said last named tube and said oscillator grid.

4. In a device of the class described, the combination of a converter having a signal amplifying portion and an oscillator section comprising a cathode, a grid and an anode, said oscillator section having a transconductance value so low that it will not oscillate at frequencies of the order of 20 megacycles per second and means for causing said section to oscillate comprising a vacuum tube having a cathode, grid and plate, a connection between the cathodes of said tubes, a circuit connecting the grids of said tubes and a circuit connecting the plate of said last named tube to the anode of said oscillator section.

5. In a device of the class described, the combination of a converter having a cathode, an oscillator grid and an oscillator anode, a signal control grid and a plate, an output circuit connecting said plate and cathode, a circuit connecting said signal control grid and cathode, means for impressing signal currents of high radio frequency on said last named circuit, shielding means interposed between said oscillator anode and said signal control grid, a tunable circuit connecting said oscillator grid and cathode, a feedback circuit coupled to said tunable circuit and connecting said oscillator anode and said cathode, and means for increasing the value of the alternating current component of the current passing through said feedback circuit above the current value passing through said oscillator ode.

, 6. In a device of the class described, the combination of a vacuum tube having a cath o d e, ag1

oscillator grid, an oscillator, ano.de,...a signal cont-rol grid and a plate, an output circuit connecting.

said cathode and plate and including means to tune said circuit to an intermediate frequency, a circuit connecting said signal control grid and cathode and including tunable means arranged to tune said circuit to desired signal currents of radio frequency, shielding means located between said oscillator grid and said signal controligrid, a circuit connecting said oscillatongrid.andcathode and including means for tuning ittqa quency differing from said signal current frequency by an amount equal to said intermediate frequency, a feedback circuit couplediofiliil t named circuit connected between said oscillator anode and cathode and means forincreasing the voltage swing of said oscillator grid above the value caused by the current of said oscillator anode passing through said feedback circuit.

WILLIAM ARTHUR HARRIS. 

